Applications of high loss dielectrics to wave guide transmission systems



March 29, 1949.

G. FERNsLE 2,465,719 APPLICATIONS OF HIGH LOSS DI ECTRICS TO.

WAVE GUIDE TRANSMISSION SYSTEMS Filed April 29, 1943 Snventor Gttorneg @wf if@ fr Patented Mar. 29, 1949 UNITED STATES ETENT OFFICE TRICS TO WAVE GUIDE SION SYSTEMS TRANSMIS- George L. Fernsler, Lawrenceville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 29, 1943, Serial No. 485,012

6 Claims. l

This invention relates generally to super-high frequency apparatus and more particularly to an improved method of and means for preventing leakage of super-high frequency energy between relatively movable conductive elements of a wave guide transmission system.

The instant invention includes improvements upon the apparatus disclosed in the copending` U. S. application of Ernest G. Linder, Serial No. 485,357, filed May l, 1943, now Patent Number 2,443,109, January 8, 1948, in which is described the use of conductive rubber having relatively low resistivity for attenuating super-high frequency energy.

Among the objects or the invention are to provide an improved method of and means for attenuating super-high frequency energy in a wave guide transmission system. Another object of the invention is to provide an improved method of and means for preventing leakage of superhgh frequency energy between relatively movable conductive elements of a wave guide system. A further object of the invention is to provide an improved method of and means for preventing leakage of super-high frequency energy along an adjusting device for a matching stub incorporated in a wave guide transmission system.

An additional object of the invention is to provide an improved method of and means for minimizing leakage of super-high frequency energy along external adjusting means for a snorting plug within a super-high frequency wave guide transmission system. Another object is to provide an improved structure for moving relatively two matching stubs along the axis of wave propagation in a super-high frequency Wave guide transmission system wherein leakage of super-high frequency energy is minimized by energy-absorptive material secured to the wave guide adjacent the relatively movable conductive elements thereof. An additional object is to provde means for sealing joints between adjacent sections of a super-high frequency wave guide to prevent leakage of energy through said joints.

The invention will be described in further detail by reference to the accompanying drawing of which Figure 1 is a cross-sectional perspective view of one embodiment thereof, Figures 2, 3, and 4 are cross-sectional views of modications of a second embodiment thereof, and Figures 5 and 6 are cross-sectional views of modifications of a third embodiment of the invention. Similar reference numerals are applied to similar elements throughout the drawing.

Figure 1 shows a wave guide I which includes a longitudinal slot 2 extending along a predetermined length of one face of the wave guide l. A U-shaped bracket .t of conductive material is shaped to conform to the outside dimensions of the wave guide i and arranged to slide longitudinally thereof. The bracket 3 includes slotted holes S, which may be employed for clamping the bracket at any predetermined position longitudinally of the wave guide i. The bracket 3 is apertured to receive a concentric transmission line 4 which may be disposed at any desired angle 'with respect thereto, The outer conductor of the transmission line l should be soldered, or otherwise electrically connected, to the bracket 3 while the inner conductor of the concentric line extends through the aperture in the bracket 3 and also through the slot 2 oi the wave guide i. It will be seen that the inner conductor of the concentric transmission line will therefore pro- Vide a wave probe for pickup of super-high frequency energy within the wave guide and that this probe may be moved longitudinally along the wave guide by shifting the U-shaped bracket 3.

A iiat layer of super-high frequency energyabsorptive material 5 such as, ior example, conductive rubber having relatively low resistivity, is secured to the inside surface of the central portion of the U-shaped bracket 3 by means of oval-headed rivets 5. The rivets 5 should preferably be irregularly spaced, and well separated from the concentric line The conductive rubber layer d will therefore occupy most of the space between the central portion of the U- shaped bracket 3 and the slotted face of the wave guide i The rubber layer should be apertured to accommodate the inner conductor of the concentric transmission line li. The rubber layer 5 will attenuate substantially all leakage energy between the wave guide and the lJ-shaped bracket 3 while the rivets t will provide electrical contact between the bracket and wave guide. Since the conductive rubber layer has relatively low resistivity, the effects of erratic contact between the movable metal parts will be minimized and will provide less interference in the concentric line output circuit, since the field near the rivets which slide on the wave guide l is relatively weak due to the high conductive currents through the rubber layer. A conductive rubber layer having a resistivity oi 5 ohm-centimeters appears to be entirely satisiatcory7 and to prevent substantially all erratic contact eifects as the probe is moved longitudinally along the wave guide. it will be seen that applicants improved structure substantially eliminates two of the most troublesome features of movable elements in super-high frequency wave guide transmission systems, since energy leakages and erratic contact between movable parts normally seriously affect the accuracy of measurements in such systems. The transmission line 4 may be connected. to a crystal detector or other utilization apparatus, not shown.

Figure 2 includes a wave guide I, having a shorting plug I2, which is movable longitudinally along the wave guide I. Adjustment of the shorting plug i2 may be accomplished externally by means of a shaft I3 which extends through a central aperture in a conductive wave guide terminating plate ifi. A knob i5, may be fastened to the external end of the adjusting shaft I3. To prevent leakage of super-high frequency energy ,past the snorting plug l2, and around the adjusting shaft I3 in the vicinity of the apertured ter-- minating plate Id, a super-high frequency attenuator is provided which effectively prevents energy leakage without affecting the operation of the snorting plug.

The attenuator includes a cylindrical conductive member It which is concentric with the adjusting shaft I3 within the wave guide I. One end of the cylindrical conductive member IS is terminated in the wave guide terminating plate lf3. A conductive rubber dielectric il occupies the space between the adjusting shaft I3 and the concentric conductive element I6. The adjusting shaft IS, concentric conductive element i5, and high-loss dielectric Il therefore comprise a coaxial transmission line of very high impedance which effectively prevents leakage of energy outside of the wave guide. Moreover, the rubber dielectric will provide a satisfactory bearing surface for adjustment of the adjusting shaft I3 for moving the snorting plug I2 longitudinally of the guide.

Figure 3 icludes wave guide :I to receive a matching stub 22 which is threaded to cooperate with a supporting member 23 disposed normal to the wave guide I. The matching stub 22 is proportioned to provide a slide lit with a conductive plug 2li which effectively seals the end of the supporting member 23 adjacent the wave guide i. In order to prevent leakage of super-high frequency energy past the joint between the conductive nlug tuning stub 22 and the supporting member 23, the remaining space within the supporting structure 23 is filled with conductive rubber 25. Therefore, the supporting structure the tuning stub 22 and the conductive rubber layer 25 provide an extremely high impedance concentric transmission line which effectively frei/ents of super-high frequency energy alc-ng the threaded tuning stub 22. The length of the portion of the tuning stub which extends into the wave guide l, may be adjusted by turning an adjusting screw bead 2l attached to the exterior end of the tuning stub 22.

Figure e includes a wave guide I having two angularly disposed stub matching sections 32, 33 which include snorting plugs 3ft, 35, respectively. 'Ihe shox-ting plugs may be of the type described in Figure 2 leakage of super-high frequency energy past the snorting plugs may be prevented in the manner described therein. Matching of a wave guide to a series of complex load circuits may be greatly facilitated by adjusting the relative spacing of the two guide matching stubs. This may be accomplished readily by providing a telescoping portion 36 of one of the lII wave guide faces whereby the stub 33 may be moved longitudinally of the guide I.

In order to prevent leakage of super-high frequency energy between the telescopic conductive face of the wave guide I and the movable guide face 36, the guide I includes a pair of cover brackets 3l, 38 to the inner surfaces of which are secured layers of conductive rubber 39, 40, respectively. Since the cover bracket 3l, the conductive rubber layer 39, the movable guide section 36 and the wave guide I are all in contact, leakage of super-high frequency energy through the telescopic joint will be attenuated effectively due to the resultant high impedance energy path. The arrangement of the cover bracket 38, the conductive rubber layer fill, the movable guide section til and guide I is similar to that just described. Therefore, the movable guide section te and tuning stub wave guide 33 may be moved in either direction longitudinally along the wave guide l to provide predetermined spacing of the guide tuning stubs 32, without involving aippreciable leakage of super-high frequency energy through the sliding joints of the wave guide.

Figure 5 includes two sections of wave guide di, which include end faces 43, M, soldered respectively thereto. This construction is conventional in wave guide systems. Ordinarily, the end plates d3, would be screwed or otherwise fastened directly together, thereby permitting considerable leakage of super-high frequency energy through the joint. However, if a washer of conductive rubber 45 is inserted between the end plates d3, fili a long leakage path having high attenuation is provided for the leakage energy, and le age through the joint is thereby effectively prevented. The conductive rubber washer d5 should be apertured for the outside dimensions of the wave guides 4l, (l2 and should also be apertured for the clamping screws It which clamp the end plates 43, M.

Figure 6 is a modification of the device described in Figure 5 wherein the conductive rubber layer l5 includes a metalli-c surface layer 41 adjacent the central aperture thereof. This metallic surface layer il may be provided by coating the rubber with a solution. comprising styrol and comminuted brass in an alcohol solution. The region of the rubber gasket i5 adjacent the center aperture therein may be coated as shown in Figure 6. If desired, the conductive layer 41 may be silver plated to provide better contact with the end plates 43, lid. Ordinary flexing of the conductive rubber gasket lli due to tighteiiing of i'I ,n "o the clamping screws im will not seriously injure the conductive coating applied in the manner described.

Thus the invention described comprises several embodiments and modifications thereof for preventing leakage of super-high frequency energy between relatively movable conductive elements a wave guide transmission system.

I claim as my invention:

l.. In super-high frequency apparatus having at least two relatively movable electrically conductive elements, a device for reducing leakage of super-high frequency energy through a space between said conductive elernents including a superhigh frequency energy absorptive member comprising a conductive rubber center having contiwicus metallic surface portions continuously occupying said space. substantially in contact with both of said conductive elements.

2. In super-high frequency apparatus including a pair of waveguides having adjacent ends thereof in close proximity, conductive flanges on said ends of said waveguides, and a super-high frequency energy absorptive member comprising a conductive rubber center having contiguous metallic surface portions occupying the space between said flanges of said waveguides.

3. Apparatus according to claim 2 including means for fastening together said ends of said waveguides 4. Apparatus according to claim 2 including a plurality of bolts projecting through said iianges and said member for fastening together said ends of said waveguides.

5. In super-high frequency apparatus including a pair of waveguides having adjacent ends thereof in close proximity, transversely externally disposed conductive flanges on said ends of said waveguides, and a device for reducing leakage 0f super-high frequency energy through a space between said ends and flanges of said waveguides including a super-high frequency energy absorptive member comprising a conductive rubber center having contiguous metallic surface portions continuously occupying said space, substantially in contact with said ends and flanges of said waveguides.

6. In super-high frequency apparatus including a pair of waveguides having adjacent ends thereof in close proximity, transversely externally GEORGE L. FERNSLER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,028,793 Mascuch Jan. 28, 1938 2,106,713 Bowen Feb. 1, 1938 2,151,118 King et al Mar. 21, 1939 2,197,123 King Apr. 16, 1940 2,253,503 Bowen Aug. 26, 1941 2,273,135 Ohnesorge et al Feb. 17, 1942 2,293,839 Linder Aug. 25, 1942 2,390,905 Wening et al Dec. 11, 1945 2,407,318 Mieher et al ..1 Sept. 10, 1946 

